Particle beam profiles for analytic equipment configuration

ABSTRACT

Beam intercept profiles are measured as a particle beam transversely scans across a probe. A current of beam particles, a detector intensity, or image pixel intensities can variously be measured to obtain the profiles. Multiple profiles are used to determine geometric parameters which in turn can be used to configure equipment. In one application, transverse beam intercept profiles are measured for different waist heights of the particle beam. Steepness of the several profiles can be used to determine a height of the probe as the height at which the profile is steepest. The known probe height enables placing the probe in contact with a substrate at another known height. In another application, transverse beam intercept profiles of orthogonal probe edges are used to position a beam waist, reduce spot size, or reduce astigmatism. Techniques are applicable to SEM, FIB, and nanoprobe systems. Methods and apparatus are disclosed, with variations.

FIELD

The disclosure pertains to particle current beam profiles, andapplications including configuration of analytic equipment.

BACKGROUND

Existing techniques for configuring analytic equipment such as scanningelectron microscope (SEM) instruments, focused ion beam (FIB)instruments, and nanoprobe instruments often involve 2-D images andhuman assessments, and can be time-consuming and error-prone.Accordingly, there remains a need for improved technology to configureanalytic instruments.

SUMMARY

Apparatus and methods are disclosed for collecting beam current profilesover a transverse scan in a particle beam machine, and applying one ormore such scans to evaluate geometric parameters which can be used inmultiple ways for automatic configuration of the particle beam machineor associated equipment.

In a first aspect, the disclosed technologies can be implemented as anapparatus incorporating a particle beam source configured to emit aparticle beam, computer-readable media storing instructions, and one ormore hardware processors with coupled memory. The hardware processorsare also coupled to the particle beam source and the computer-readablemedia. When executed by the one or more hardware processors, theinstructions cause the hardware processors to perform operationsincluding obtaining a plurality of transverse profiles of particle beamintensity and evaluating the transverse profiles to establish ageometric characteristic. The transverse profiles are obtained at one ormore longitudinal positions of a waist of the particle beam.

In some examples, a transverse profile can be obtained by measuringcurrent of the particle beam intercepted by a current collector at aplurality of points of a transverse scan: the particle beam can bescanned across the current collector, or the current collector can bescanned across the particle beam. In further examples, a transverseprofile can be obtained by measuring intensities of secondary orbackscattered particles at a plurality of points of a transverse scan ofthe particle beam and a probe, relative to one another. In additionalexamples, a transverse profile can be obtained by determining pixelintensities, with an imaging subsystem, along a transverse scan of theparticle beam relative to a probe.

In certain examples, establishing the geometric characteristic can bedetermining a longitudinal coordinate of a probe. The probe can be ananoprobe, and the apparatus can include an actuator coupled to thenanoprobe. The operations can include determining a longitudinaltranslation of the nanoprobe based on a difference between thelongitudinal coordinate of the nanoprobe and a longitudinal coordinateof a substrate surface. Based on the longitudinal translation, theactuator can be controlled to place the nanoprobe in contact with thesubstrate surface.

In further examples, establishing the geometric characteristic can besetting a longitudinal coordinate of the waist of the particle beam.First and second transverse profiles can include respectively transversescan points of the particle beam relative to first and second probeedges. The first and second probe edges can have orthogonal transverseprojections. The first and second transverse profiles can be obtained ina single transverse scan. The scan speed of the single transverse scancan be faster when the particle beam is at one of the two probe edgesand slower when the particle beam is between the two probe edges. Inadditional examples, the operations can include executing a controladjustment on the particle beam to reduce an astigmatism or a waist sizeof the particle beam.

In various examples, the apparatus can be a scanning electronmicroscope, the particle beam can be a focused ion beam, or the currentcollector can be a nanoprobe.

In another aspect, the disclosed technologies can be implemented as amethod. Multiple transverse beam intercept profiles are obtained forrespective longitudinal positions of a waist of a particle beam. Each ofthe transverse beam intercept profiles is obtained with a probe at leastpartly intercepting the particle beam. The transverse beam interceptprofiles are evaluated to determine a longitudinal coordinate of theprobe.

In certain examples, a transverse beam intercept profile can be obtainedby measuring current of the particle beam intercepted by the probe at aplurality of points of a transverse scan of the particle beam relativeto the probe. Evaluation can include determining an indicator ofsteepness for each of the transverse beam intercept profiles, andthereby determining a first longitudinal coordinate of the waist of theparticle beam, at which the steepness is a maximum. In some examples,the first longitudinal coordinate of the waist can be determined byfitting a measure of the steepness as a function of the longitudinalposition of the waist of the beam. In other examples, the firstlongitudinal coordinate of the waist can be determined by iterating thelongitudinal positions of the waist of the particle beam until aconvergence criterion is met. The longitudinal coordinate of the probecan be determined based on the first longitudinal coordinate of thewaist. The method can include determining an amount of longitudinaltranslation for the probe, from a difference between the longitudinalcoordinate of the probe and a longitudinal coordinate of a substratesurface. The probe can be directly or indirectly be longitudinallytranslated by the determined amount.

In further examples, the abovementioned transverse beam interceptprofiles can be obtained after tuning a cross-sectional pattern of theparticle beam. The tuning can be performed based on other transversebeam intercept profiles.

In additional examples, the particle beam can be an electron beam of ascanning electron microscope; and the probe can be a nanoprobe. Atransverse beam intercept profile can be obtained by measuring currentof the particle beam intercepted by the probe at a plurality of pointsof a transverse scan of the particle beam relative to the probe. Thetransverse beam intercept profile can correspond to a portion of theparticle beam intercepted by the probe as a function of a transversecoordinate. Evaluation of the transverse beam intercept profiles caninclude determining an indicator of steepness for each of the transversebeam intercept profiles, determining a first longitudinal coordinate ofthe waist of the particle beam at which the steepness is a maximum, anddetermining the longitudinal coordinate of the probe based on the firstlongitudinal coordinate of the waist. The method can be implemented by acomputer-readable storage media storing instructions which can beexecuted by one or more hardware computer processors.

In another aspect, the disclosed technologies can be implemented as amethod. Multiple transverse beam intercept profiles are obtained forrespective having distinct orientations. Each of the profiles isobtained with the respective probe edge at least partly intercepting aparticle beam. The transverse beam intercept profiles are evaluated toset one or more geometric parameters of the particle beam.

In some examples, a transverse beam intercept profile can be obtained bymeasuring current of the particle beam intercepted by a given one of theprobe edges at a plurality of positions of a transverse scan of theparticle beam relative to the given probe edge. The geometric parameterscan include a longitudinal coordinate of a waist of the particle beam.The longitudinal coordinate of the waist can be set to a longitudinalcoordinate of a transverse plane in which the probe edges are situated.The method can include adjusting one or more astigmatism controls toreduce the waist of the particle beam.

In additional examples, two of the probe edges can have orthogonaltransverse projections. Evaluation of the transverse beam interceptprofile can include identifying first and second values of a focuscontrol of the particle beam at which the transverse beam interceptprofiles of the two probe edges are complementary.

In certain examples, the particle beam can be an electron beam of ascanning electron microscope and can have a waist. The two probe edgescan be edges of one or more nanoprobes. A transverse beam interceptprofile can be obtained by measuring current of the particle beamintercepted by a given one of the two probe edges at multiple positionsof a transverse scan of the particle beam relative to the given probeedge. The multiple positions can be situated on a straight line.Geometric parameters including a longitudinal coordinate of the waistand a diameter of the waist can be set. The method can further includedetermining a central value between the first and second values of thefocus control, setting the focus control to the central value, therebysetting the longitudinal coordinate of the waist at a transverse planeof the two probe edges by. Settings of one or more astigmatism controlsof the particle beam can be iterated to minimize the diameter of thewaist. The method can be implemented by a computer-readable storagemedia storing instructions which can be executed by one or more hardwarecomputer processors.

The foregoing and other features and advantages of the disclosedtechnologies will become more apparent from the following detaileddescription, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B are diagrams illustrating an application of the disclosedtechnology.

FIG. 2 is a flowchart of an example method according to the disclosedtechnologies.

FIG. 3 is a flowchart of a variation of the example method of FIG. 2.

FIG. 4 is a flowchart of an example method according to the disclosedtechnologies.

FIG. 5 is a graph illustrating example methods of determining alongitudinal coordinate of a probe according to the disclosedtechnologies.

FIG. 6 is diagram of a representative apparatus suitable for practicingsome examples of the disclosed technologies.

FIGS. 7A-7D are diagrams illustrating an application of the disclosedtechnologies.

FIG. 8 is an oblique view of an example astigmatic beam.

FIG. 9 is a flowchart of an example method according to the disclosedtechnologies.

FIG. 10 is a flowchart of an example method according to the disclosedtechnologies.

FIG. 11 is a flowchart of an example method according to the disclosedtechnologies.

FIG. 12 illustrates a generalized example of a suitable computingenvironment in which described embodiments, techniques, and technologiescan be implemented.

DETAILED DESCRIPTION Introduction

SEM, FIB, nanoprobe, and other forms of analytic equipment can useparticle beams along with probes or other apparatus. Conventionalconfiguration of such equipment often involves procedures that can beslow or prone to error, for example acquiring a 2-D raster scannedimage, or relying on human interpretation of such an image. Suchprocedures can prevent implementation of rapid, consistent,reproducible, or automated analytic workflows, which can be ofparticular concern in a production environment.

Examples of the disclosed technologies can apply geometric properties ofparticle beams or probes to make an automated determination of othergeometric parameters, which in turn can be used for automatedconfiguration of analytic equipment.

As an example, nanoprobe systems can offer precise relative motion of ananoprobe, but can have difficulty accurately assessing an absoluteposition of the nanoprobe, in particular, the height of the nanoprobeabove a substrate surface. With the disclosed technologies, the heightof a nanoprobe can be determined and used to accurately set thenanoprobe down on a substrate surface.

Existing particle beam controllers can have a capability to create afocused beam, with the ability to control and monitor the workingdistance. A focused beam can have a waist at which the cross-sectionalspot size is minimum, with increasing spot sizes at locationslongitudinally displaced from the waist in either direction. Thus,scanning a current measuring probe through the beam waist can result ina steeper profile of measured intercepted beam current, as compared toscans through other cross-sections of the beam. The disclosed technologyapplies this property by acquiring transverse beam intercept profiles atseveral working distances (longitudinal coordinates) of the beam waist.A longitudinal coordinate L0 of the waist, at which the transverse beamintercept profile is steepest, indicates that the probe also has alongitudinal coordinate L0. In an example, L0 was determined with anaccuracy within 1 μm.

In examples, this technique can be performed with 3-20 transverse scansat different working distances, which can be obtained significantlyfaster than hundreds or even a thousand scan lines in a typical 2-Draster scan image. Because this technique can be automated, it can befast and consistent. Moreover, this technique does not rely on focusedimages, and can be used when the nanoprobe is fairly close to thesubstrate surface, a condition which can be particularly challengingwith a conventional image-based approach.

As another example, particle beam machines commonly require tuning ofthe beam to obtain a good quality beam, e.g., having a narrow waist andlow or zero astigmatism. Conventional approaches can involve evaluationof images or human assessment, which can be slow or error-prone. Withthe disclosed technologies, single line scans across two probe edges canbe used to assess characteristics of a beam's focus or astigmatism onthe basis of which automated beam tuning can be performed, as describedherein.

Such a technique, using a single line scan or a few line scans, canoffer a significant saving over 884 scan lines in a typical imageformat. The technique can be widely applied to a variety of particlebeam equipment.

The disclosed technologies can provide valuable improvements toautomated workflow for particle beam based analytic equipment.

Terminology

The usage and meaning of all quoted terms in this section appliesthroughout this disclosure unless clearly indicated otherwise orrepugnant to the context. The terminology below extends to related wordforms.

The term “actuator” refers to a mechanical device for moving anotherobject. Some actuators can be classified as rotary or linear actuators.Actuators often take one form of energy (e.g., electrical energy) andconvert it into mechanical energy. Some actuators that can be used withthe disclosed technology are piezoelectric actuators.

The term “ammeter” refers to a measurement device that can measureelectrical current. An ammeter can be embodied as a stand-alone device,as part of an electronics package, or even within a same integratedcircuit package (e.g., system on a chip (SoC)) as a microprocessor orother computer processors. An electronic ammeter can include e.g., aresistor coupled to a voltage-sensing analog-to-digital converter (ADC),a current-sensing ADC, or another implementation. An ammeter can havemultiple inputs which can be measured separately (e.g., a four-channelammeter) or together (e.g., so-called wired-OR configuration).Accordingly, a group of distinct ammeters is also considered to be anammeter.

The term “astigmatism” refers to the deviation from circularity of abeam cross-section. In simple examples, a non-circular beamcross-section can be characterized as an ellipse having a major axis(“a”, longest distance across the beam), a minor axis (“b”, shortestdistance across the beam), and an orientation of the major axis relativeto some reference direction such as an X axis. The eccentricity of theellipse is e=√{square root over (1−b²/a²)}. The astigmatism can becharacterized by eccentricity and orientation, or other equivalentparameters. Astigmatism of a beam can vary with longitudinal position.

The term “beam” refers to a directional flow of particles or energy.Common beams of interest in this disclosure are electron beams or ionbeams, but the term is not limited thereto. A beam can have finiteextent transverse to its principal longitudinal direction of flow. Aline joining the centroids of two or more transverse cross-sections of abeam is an “axis” of the beam. Some beams can be well-confined. Otherbeams can have tails, with transverse extent beyond the bulk of thebeam's particles or energy. Accordingly, a beam or any cross-section ofthe beam can have a “boundary” which can be defined as a smallestperimeter or surface containing some fraction of the beam's particles orenergy, such as 90%, 99%, 100%, or some other fraction. The dimensionsof the beam (such as diameter, area) or related quantities such aseccentricity or astigmatism can be defined with respect to the boundary.A beam can have a uniform or non-uniform density distribution across itscross-section. Such a distribution is called a “pattern” of the beam.Some beams of interest can have or can be approximated by a Gaussianpattern. A beam can have a waist.

Terms such as “best,” “lowest,” “minimum,” “optimize,” or the like areused to indicate that a selection among a few or among many alternativescan be made, and such selections need not be better, lower, less, orotherwise preferable to other alternatives not considered.

A “coordinate” is a number, optionally with a unit, that indicates aposition or orientation of a point or object in space. Commoncoordinates can be linear (e.g., longitudinal coordinate in thedirection of a beam axis) or angular (e.g., an angle in cylindricalcoordinates).

The term “current” refers to electrical current for charged particlebeams, but can also refer to equivalent electrical current for, e.g.,neutral or optical beams, either of which can, under suitableconditions, generate electrical current in a target material through aprocess such as ionization or the photoelectric effect. “Interceptedcurrent” refers to the current measured by an ammeter coupled to anobject such as a probe inserted at least partly within a beam tointercept at least a portion of the beam. In some examples, interceptcurrent can equivalently be determined by subtracting substrate currentfrom the total beam current. That is, a measurement of beam currentintercepted by a probe need not measure the current directly from theprobe. Other proxies for intercepted beam current can also be used, forexample detected intensity of secondary or backscatter particles from aprobe or from a substrate, or pixel intensity obtained in an imagingsystem from such detected secondary or backscattered particles. Any ofthese, or another physical phenomenon, can serve as an indicator ofintensity of a particle beam.

The term “current collector” refers to any object which can be insertedat least partly within a beam to produce a current.

The term “dwell” refers to an operation of stopping or moving slowly atpart of a scan or cycle relative to other parts of the scan or cycle.The term “dwell time” can refer to the amount of time to perform aportion of a scan, which can be a single current measurement at aparticular coordinate position, or which can be a succession ofmeasurements to gather a single intercept profile of one probe edge, ina scan over multiple probe edges. In contrast, “transit time” can referto the amount of time taken to move the beam or probe from onemeasurement point to a next measurement point, or from one portion of ascan (e.g., over a first probe edge) to another portion of the same scan(e.g., over a second probe edge).

The term “establish” refers to forming a correspondence between avariable quantity and a value. In some examples, the correspondence canbe formed by determining a present value of the variable quantity. Inother examples, the correspondence can be formed by adjusting thevariable quantity to have a target value.

The term “focus” refers to a position in a beam at which an image hasbest resolution (which can be the same as the waist of the beam), orrefers to a property of an image having been formed at the focus of abeam. A focus can be zero-dimensional (a point), one-dimensional (acurve or line), or two-dimensional (a surface or plane).

The term “focused ion beam” (FIB) refers to a beam of ions whose focuscan be controlled to, for example: focus at a spot on a surface, have afocused waist at another longitudinal coordinate, or scan over a scanpattern. A FIB can be used for analysis, deposition, or removal ofmaterial at the focus spot. Commonly, a FIB comprises positive elementalions, such as Xe+ or Ga+, however these are not requirements. Ion beamspecies such as Ga+ can be sourced from e.g., a liquid metal ion source(LMIS), while other ion beam species such as Xe+ can be produced in aplasma. A FIB produced with a plasma source can be termed a plasmafocused ion beam (PFIB). Commonly, a FIB can be directed onto a surfacefor an analysis, deposition, imaging, or removal procedure.

The term “geometric characteristic” refers to any property or parameterof a physical object, apparatus, or system, which can be measured inunits of length, as a spatial angle, or as a function of only suchquantities (including areas and volumes). Some geometric characteristicsof interest in this disclosure include waist size of a beam, astigmatismof a beam (including eccentricity and orientation), longitudinalcoordinate of a probe, cross-sectional area of a beam, or longitudinalcoordinate of a beam waist.

The term “intercept” refers to absorbing or redirecting a portion (orall) of a beam. For example, a current collector placed partway into anelectron beam can intercept some percentage of the beam and route theintercepted current to an ammeter for measurement.

The term “iteration” refers to each of multiple times a given operationor sequence of operations is performed. A sequence of iterations isdubbed a “loop.” Iterations can be classified as “identical” ifparameters are left unchanged between iterations (identical iterationscan be used, for example, to improve signal quality through averaging),“predetermined” if the parameter values over which operations are to berepeated are known before the first iteration is performed, or “guided”if a parameter value of a later iteration depends on a result of anearlier iteration. Predetermined iterations refer to iterations actuallyperformed. A loop of predetermined iterations need not execute for allthe predetermined parameter values, but can terminate or exit early if atermination condition is met. A loop of guided iterations can begin withone or more predetermined iterations as seed(s).

The terms “longitudinal” and “transverse” generally describe coordinatesof the described examples. Longitudinal refers to a direction along anaxis of a beam, an axis of a beam source, or an axis of an instrument.Positions along the longitudinal direction can be described as height(measured above a substrate), longitudinal coordinate, Z coordinate,working distance (the distance from an emitting aperture or plane of abeam source to the waist or focus of the beam), or simply longitudinalposition.

The term “nanoprobe” refers to an electrical probe suitable forinvestigating microelectronic devices with feature size under 1 μm andoften under 100 nm. In some examples, nanoprobes can be deployed withSEM, FIB, or atomic force microscopy (AFM) systems to assist inregistration between nanoprobe and substrate features. Nanoprobes cancommonly be arranged in an array of two to eight nanoprobes. In someexamples, a nanoprobe can have a tip radius of 5 to 35 nm, and a bodydiameter of about 100 to 500 μm. A nanoprobe can be coupled toinstrumentation circuitry to provide stimulus or acquire responsesignals from a substrate under test. A nanoprobe coupled to an ammetercan be used to acquire beam intercept current profiles in some examplesof the disclosed technologies.

The term “orthogonal” refers to two directions, features, or objectsthat are perpendicular or nearly perpendicular to one another. Forfeatures or objects, a direction of major extent can be considered fordetermination of orthogonality. In examples, two directions can be saidto be orthogonal if they are within a defined tolerance of 90°, such as90°±1°, 90°±2°, 90°±5°, 90°±10°, 90°±20°, or 90°±30°.

The term “particle” refers to a distinct unsubdivided unit of a flow ofmatter. Particles of common interest in this disclosure include chargedparticles such as electrons or ions (such as Ga, Xe, or protons),however particles are not limited thereto.

The term “particle beam” refers to a beam comprising a directional flowof particles.

The term “probe” refers to a device used in analytic equipment to applyor receive a signal at a particular position. Probes can be used toinvestigate a substrate, or to profile a particle beam. Inasmuch asprobes in this disclosure can be used to measure beam current, in manycases a probe can serve as a current collector. A probe can haveadditional functions in analytic equipment, such as a nanoprobe. Acurrent collector need not have any additional functions. A nanoprobe isa particular example of a probe. Additionally, a width of a probe can be1-2 orders of magnitude bigger than a transverse dimension of a particlebeam. Accordingly, in some examples, a transverse beam intercept profilecan be complete after only a small portion of a probe has passed intothe beam. Therefore, in some instances a probe edge is described herein.The “edge” of a probe or another current collector is a bounding curveof the probe or current collector as viewed in a longitudinal directiondefined by a particle beam, and portions of the probe or currentcollector adjacent to the bounding curve. The edge portion of the probecan have a width extent of 0.1% to 33% of the width of the probe, oroften at least the width of a particle beam that is used with the probe.Accordingly, descriptions of a probe herein can similarly be applicableto an edge of a current collector, an edge of a nanoprobe, or an edge ofanother probe. Relative to a transverse scan, the edges of a probe canbe further labeled as “leading edge,” which intercepts a portion of abeam first during a transverse scan, and a “trailing edge” whichintercepts a portion of the beam last during a transverse scan. Theleading edge and the trailing edge can be reversed if a scan directionis changed. The terms “leading edge” and “trailing edge” can be extendedto corresponding portions of a beam intercept profile.

The term “profile” refers to a distribution of some quantity as afunction of position along a straight or curved line. A common profileof interest in this disclosure is a profile of intercepted current of aparticle beam as a function of a transverse coordinate (e.g., X) as aprobe or current collector and a beam move with respect to each other inthe X direction. Such a profile is referred to as a “transverse beamintercept profile.” The particle beam can propagate in a longitudinaldirection.

The term “scan” refers to a spatial traversal. Common scans in thisdisclosure are one-dimensional scans, such as a transverse scan of aprobe in an X direction across a particle beam, and often with attendantmeasurements being performed during the scan, such as measurement ofcurrent as the probe traverses the particle beam. However, neither ofthese are requirements: a scan can be two or more dimensions, and neednot involve any measurement. A scan can be continuous, for example withmeasurements performed continuously as a probe is moved, or discrete,for example with measurements made at a set of discrete, distinctpoints. Whether a scan is continuous or discrete, the scan can beperformed with uniform or variable speed. A scan can be monotonic, forexample a scan over multiple points having successively increasing Xcoordinate values, or not. In some examples, the points of a scan can betraversed back-and-forth, or out-of-order in another sequence. Aone-dimensional scan can be performed over a plurality of points orpositions that are disposed on a straight line.

The term “scanning electron microscope” (SEM) refers to an instrumentcombining an electron beam with controls to scan the electron beam inone or more transverse directions to perform imaging or some otheranalytic function on a substrate. An SEM can be used as a stand-aloneimaging instrument, or can be integrated with other analytic equipment,for example in a nanoprobe system.

The term “steepness” refers to a quantitative attribute of a signal orprofile: a measure of steepness can be inversely proportional to thedistance over which the signal or profile rises or falls. Taking X to bea distance coordinate in a scanning direction, and Q as a signal ofinterest, example steepness measures can include maximum slope dQ/dX,reciprocal of the transition distance ΔX between two limits such as 10%to 90% of a flat-top or peak value of the signal Q, the average slopeΔQ/ΔX over similar limits, or an absolute value of any of thesemeasures. Other measures of steepness can be reciprocals of thesequantities, for example, the transition distance ΔX. For the lattercase, maximum steepness can be at a minimum value of ΔX. That is,searching for the steepest profile can involve searching for a minimumvalue of the steepness measure ΔX, as in FIG. 5 herein. Any of these orsimilar measures can provide an indication of steepness. While ΔX of aprofile can be used as a steepness measure, in other instances ΔX can bemerely a difference between two X coordinates, without reference tosteepness.

The term “substrate” refers to a physical object that can subject to ananalytic procedure with a beam or probe or other analytic equipment asdescribed in this disclosure. The term “sample” can be usedinterchangeably. Often, a substrate can have a “major surface” exposedto the beam or probe, which is a surface of the substrate whose area isnot substantially exceeded by any other surface of the substrate.

The terms “top,” “bottom,” “up,” “down,” and the like are used forconvenience, with respect to a common configuration in which a topsurface of a sample is processed, e.g., by ion milling, downward toincreasing depths. One of ordinary skill will understand from thisdisclosure that a choice of actual orientation can be varied withoutdeparting from the scope of the disclosed technologies.

The term “translation” refers to a change in position of a physicalobject. Although a translation from coordinates (x1, y1, z1) to (x2, y2,z2) can be performed in a straight line (i.e., as a “lineartranslation”), there is no requirement to do so unless expressly stated.A translation can be performed in a circular, sinuous, or other path.Similarly, a translation neither requires nor precludes any change inorientation. However, a change in orientation without a change inposition is not considered a translation.

The term “transverse” refers to dimensions and positions in any planeperpendicular to a beam axis. A substrate surface can often be orientedto be transverse to the beam, but this is not a requirement. In someexamples, the direction along which a transverse scan is performed canbe regarded as the X direction without loss of generality. In otherexamples, scans can be performed in more than one transverse direction.In some examples, the orientation of an edge of a current collector orprobe can be regarded as the Y direction, i.e., orthogonal to thetransverse scan direction but in the transverse plane, while in otherexamples such an edge or probe can have a different orientation, such asat 45° from the X direction.

The term “transverse projection” refers to a projection of an object orfeature onto a transverse plane. That is, the transverse projectionappears as the shadow of the object or feature on the transverse planewhen subject to an illumination beam propagating in the longitudinaldirection.

A “transverse scan” refers to a scan over a varying transversecoordinate, for example a probe or a beam moved in a transversedirection relative to the other. Measurements at points of a transversescan can yield a transverse profile.

The term “waist” refers to a longitudinal position in a beam at whichthe transverse cross-section can fit inside a smaller circle than thetransverse cross-section at any other longitudinal position. A beamwaist can be characterized by a pattern, a diameter, or across-sectional area (sometimes dubbed “spot size”). In a beam havingastigmatism, the waist can be similar to the circle of least confusionused in optics.

First Example Application

FIGS. 1A-1B are diagrams illustrating an application of the disclosedtechnology. Each diagram illustrates a transverse beam interceptprofile, plotted as a graph of measured probe current I vs. transversecoordinate X, for respective configurations. The transverse coordinate Xcan be scanned either by sweeping the beam in the X direction or bytranslating the probe in the X direction.

FIG. 1A illustrates a configuration in which beam waist 137 has alongitudinal coordinate 139 (Zw) close to the longitudinal coordinate149 (Zp) of probe 145. Graph 110 shows the response of the interceptedbeam current I as a function of a transverse coordinate X, with fivepoints 111-115 marked for purpose of illustration. The actual number ofpoints measured for a graph such as 110 can vary, and can be more thanfive or less than five. The insets 121-123 show the configuration of theprobe 145 and the beam 135 for the respective points 111-113. Featurescommon to the insets 121-123 are omitted from the insets 122-123 forclarity of illustration. Coordinate axis X is marked in the inset 121from the perspective of the beam 135 being scanned with the probe 145stationary. A typical beam diameter can be in a range from 1 nm to 1often about 1-2 nm at a beam waist, whereas a typical probe diameter canbe in a range from 50-2000 often about 200-500 μm. Accordingly, theinsets 121-123, 181-183 of FIGS. 1A-1B are illustrative and not toscale.

At point 111, the probe 145 is outside the beam 135, and the interceptedcurrent is very small and can be approximated as zero. At intermediatepoint 112 the probe has penetrated approximately half way into the beamwaist 137, and the intercepted current is about half the total beamcurrent. At point 113, the probe 145 can block the beam completely, andthe intercepted beam current I can be equal or very nearly equal to thetotal beam current, with some possible small correction due to effectssuch as tails of the beam, or scattering. Two additional intermediatepoints 114-115 are marked, for which intercept beam current can be about20% and about 80% of the total beam current. Because the beam spot sizeat coordinate Zp 149 is similar to the spot size at the beam waist 137,and can be small, the change in transverse coordinate between points114, 115 can also be small, resulting in a steep beam intercept profile.Any of ΔI/ΔX, 1/ΔX, ΔX, or another measure of steepness can be used tocharacterize the steepness of graph 110 (ΔX, ΔI being measured betweenparticular points on graph 110). In some examples, a scan can beperformed with predetermined iterations, while in other examples, a scancan be guided to obtain target points on the beam intercept profile,such as at 20% or 80% of the total beam current, or other preselectedtarget points.

FIG. 1B illustrates a configuration having a larger separation betweenlongitudinal coordinates 138, 149 of the beam waist 137 and the probe145, as compared to FIG. 1A. Graph 170 shows the response of theintercepted beam current I as a function of a transverse coordinate X,with five points 171-175 marked. The insets 181-183 show theconfiguration of the probe 145 and the beam 136 for the respectivepoints 171-173. Similar to insets 121-123, the insets 181-183respectively show intercepted currents nearly zero, about half of thetotal beam current, and nearly all of the total beam current. However,because the probe 145 and the beam waist 137 are farther separated inthe Z direction, the spot size traversed by the beam in FIG. 1B islarger than in FIG. 1A, and consequently the transverse separation ΔXbetween points 174-175 can be significantly larger than thecorresponding transverse separation ΔX of FIG. 1A.

By evaluating steepness for different longitudinal coordinates of beamwaist 137, a longitudinal coordinate L0 having the steepest profile canbe found (described further with reference to FIG. 5 herein), and thelongitudinal coordinate of the probe can be set equal to L0. Withsuitable beam quality, the disclosed technology can providedetermination of L0 with accuracies within 10 μm, 1 μm, or 0.1 μm.

First Example Method

FIG. 2 is a flowchart 200 of a first example method according to thedisclosed technologies. In this method, transverse beam profiles can beused to determine a longitudinal coordinate of a probe. The transversebeam profiles can result from the probe intercepting a portion of aparticle beam over a series of points along a transverse scan.

At process block 210, a loop can be iterated over a sequence oflongitudinal positions of a beam waist. Block 211 indicates theoperations that can be performed at each iteration of the loop 210. Atprocess block 212, the waist of a particle beam can be positioned at theinstant longitudinal position. At process block 214, a transverse beamintercept profile can be obtained with a probe at least partlyintercepting the particle beam.

At process block 220, the transverse beam intercept profiles can beevaluated to determine a longitudinal coordinate of the probe. Numerousvariations can be used. For example, process block 230 indicates animplementation of process block 214 which can be used in some examples.At process block 230, a loop can be iterated over a sequence of pointsof a transverse scan between the particle beam and the probe. Block 231indicates the operations that can be performed at each iteration of theloop 230. At process block 232, the waist of a particle beam can bepositioned at the instant transverse position. At process block 234, thebeam current intercepted by the probe can be measured. Collectively, themeasured beam currents can form the transverse beam intercept profile ofblock 214.

As another possible variation, process blocks 240, 250 indicate animplementation of process block 220. At process block 240, a loop can beiterated over the transverse beam intercept profiles collected atprocess block 210. Block 241 indicates that, for each profile, anindicator of steepness can be determined. Then, at process block 250, alongitudinal coordinate of the particle beam waist can be determined atwhich the steepness is maximum. In some examples, such a determinationcan be made by fitting a measure of the steepness as a function of thelongitudinal position of the beam waist, as shown at process block 253.At process block 260, the longitudinal position of the probe can bedetermined based on the longitudinal coordinate determined at block 250.

FIG. 3 is a flowchart 300 of yet another variation in which collectionand evaluation of transverse beam intercept profiles go hand in hand inan iterative procedure. At process block 310, a loop can be iteratedover a sequence of longitudinal positions of a beam waist. Processblocks 311, 312, 314 can function similarly to process blocks 211, 212,214 described herein.

Then, at process block 316, a steepness of the instant transverse beamintercept profile can be evaluated, similarly to process block 241. Atprocess block 318, the steepness can be used to determine a nextlongitudinal waist position, for which block 311 can be repeated. When atermination condition is met, loop 310 can terminate, and thelongitudinal position of the probe can be determined. In examples, thetermination condition can be based on a number of iterations of loop310, convergence of the longitudinal waist position to within atolerance, or another condition. In some examples, the longitudinalposition of the probe can be determined based on the final longitudinalposition of loop 310.

Further variations can also be employed. The method of flowcharts 200 or300 can be preceded by tuning a cross-sectional pattern of the particlebeam, for example, to minimize astigmatism or to minimize waist size. Insome examples, this tuning can be performed based on additionaltransverse beam intercept profiles, as described herein.

In other examples, the method of flowcharts 200 or 300 can be followedby calculating a translation amount for the probe, based on a differencebetween the probe's longitudinal coordinate and a longitudinalcoordinate of a substrate surface. The probe can be translated by thistranslation amount, and the probe can be brought into contact with thesubstrate surface.

Second Example Method

FIG. 4 is a flowchart 400 of a second example method according to thedisclosed technologies. In this method, the height of a nanoprobe can bedetermined, using a particle beam, and used to position the nanoprobe ona substrate.

At process block 410, the longitudinal coordinate of a substrate along alongitudinal axis of the particle beam can be determined. This can beaccomplished using a focused beam or optical image of the substrate, orby another technique.

At process block 420, a loop is performed over multiple longitudinalpositions of a waist of the particle beam. Block 421 indicatesoperations that can be performed in the loop for each longitudinalposition of the beam waist. At process block 422, the waist of theparticle beam can be configured to be at the current longitudinalposition. Then, at process block 424, a relative transverse scan betweenthe nanoprobe and the beam can be performed. Concurrently, interceptedbeam current can be measured to obtain the beam intercept profile asindicated at process block 426. At process block 430, the beam interceptprofiles can be evaluated, to obtain the longitudinal coordinate of thenanoprobe at process block 440. In some examples, the evaluation of beamintercept profiles can be done in during the iterations of loop 420, andcan be used to guide successive iterations of loop 420, similarly tothat described in context of FIG. 3. For example, if successiveiterations have passed through a longitudinal beam waist position havingmaximum steepness (e.g., successive longitudinal waist positions in afirst direction had increasing steepness and then decreasing steepness),a next iteration of loop can change the longitudinal waist positionopposite to the first direction, and can reduce the longitudinalposition step size for subsequent iterations.

With longitudinal coordinates of both the nanoprobe and the underlyingsubstrate known, a longitudinal translation amount (i.e., a distance)for the nanoprobe can be calculated at process block 450. In examples,the translation amount can be the difference of the two longitudinalcoordinates, plus or minus a small offset. Offsets can vary between 10nm to 100 μm, for example, between 20 nm to 1 μm, or between 1 μm to 20μm. A positive offset can ensure positive contact between the nanoprobeand the substrate, that is, with modest pressure, and can compensate formeasurement errors or unevenness of the substrate surface. A negativeoffset (i.e., an offset subtracted from the difference betweenlongitudinal coordinates) can account for finite size of the nanoprobein the longitudinal direction. At process block 460, the calculatedtranslation can be applied to the nanoprobe, for example, by control ofactuators coupled to the nanoprobe, to bring the nanoprobe into contactwith the substrate at block 470. As a variation, all or part of thetranslation can be applied to the substrate instead of the nanoprobe.

Example Determination of Longitudinal Coordinate of a Probe

FIG. 5 is a graph 500 illustrating example methods of determining alongitudinal coordinate of a probe according to the disclosedtechnologies. The graph 500 plots ΔX, which can be a steepness measure,as a function of longitudinal position Zw of a beam waist (see also FIG.6). With ΔX used as a steepness measure, smaller values of ΔX canindicate a steeper profile. That is, maximum steepness corresponds to aminimum on curve 510. Each point 531A-533D of the curve 510 represents arespective transverse scan at the corresponding waist position. Othersteepness measures can be used, some associated with an inverted shapecompared to curve 510, and requiring a determination of a maximum valueof steepness.

In some embodiments, a series of transverse scans can be performed toobtain e.g., the points labeled 531A-531E, and a curve 510 can be fittedto these points using a least squares or other fitting algorithm. Thefitted curve 510 can be a polynomial (such as a parabola), a rotatedhyperbola, or another function. Polynomial fits can be performed usingclosed-form matrix calculations; other fits can be evaluated using theLevenberg-Marquardt method or another iterative numerical algorithm. Thefitted curve can be used to determine the waist height, at which ΔX isminimum (maximum steepness), and which can be assigned to thelongitudinal coordinate of the probe Zp.

In other embodiments, transverse scan points can be obtained by guidediterations. FIG. 5 illustrates one such example using a converging5-point scan. On a first pass, points 531A-531E can be obtained fromrespective scans. The positions Zw for points 531A, 531E can be chosenfar enough apart to bracket the sought minimum Zp. For example, point531E can be measured with the waist set to be at or below a height ofthe substrate. Point 531A can be measured with the waist set near theparticle beam source, at a height inaccessible to the probe. Examinationof the points 531A-531E shows that, among these points, the steepnessfactor is minimum at 531C, and that the minimum is bracketed by 531B,531D. Thus, the next iteration can zoom in on the region 531B-531D.Because 531C has already been evaluated, only points 532B, 532D need tobe obtained. Because 531C is still minimum, a third iteration can beperformed, adding 533B, 533D between new endpoints 532B, 532D.Eventually a termination condition can be reached, such as the spacingof waist positions Zw between adjacent points 531C, 533D being below athreshold, and the coordinate Zp can be determined as e.g., the measuredpoint having maximum or minimum value of a steepness measure.

Iterative techniques for determining a point of maximum steepness can becombined. In some examples, a single scan sweep can be used to determinea waist position at which steepness is maximum, followed by an iterativesearch using progressively smaller step sizes. Other techniques andcombinations of techniques can also be used.

Example Apparatus

FIG. 6 is a diagram of an apparatus 600 suitable for practicing someexamples of the disclosed technologies. The apparatus 600 can beanalytic instrumentation for investigating a substrate 660 and itsattendant features or devices. Substrate 660 is generally not part ofthe apparatus 600, and accordingly is shown by a dashed outline.However, apparatus 600 can include a mount, translation stage, loadlock, or other fixturing or handling devices (not shown) to assist inhandling the substrate 660.

Apparatus 600 can be controlled by computer 610, which can incorporateone or more hardware or virtual processors as described further herein.Computer 610 can execute instructions stored on computer-readable mediato control the apparatus 600 and perform the operations describedherein. Computer 610 can have a bus or network connection 613 toperipheral devices (e.g., printer, storage, display) or to othercomputers (not shown). Apparatus 600 can include the followingoperational units coupled to the computer 610: a particle beam source630, one or more actuators 640, and one or more ammeters 650. Alsorelevant to the disclosed technologies is a probe 645, shown as across-section, which can variously be part of apparatus 600, or providedseparately. Probe 645 can be a nanoprobe. In some embodiments, multipleprobes or nanoprobes can be used, however, for simplicity ofillustration, only one probe 645 is depicted in FIG. 6. The actuators640 can be coupled to adjust the position of the probe 645; a physicalconnection is schematically represented by arrow 641. The probe 645 canbe coupled to the ammeter by an electrical conductor 650, which can be awire. In some examples, a particle detector 670 (which can be coupled toan imager) can be used to detect backscattered or secondary electrons678 from probe 645 or from substrate 660, as described further herein.

Particle beam source 630 can be configured to emit a particle beam 635.The particle beam 635 can be a focused beam, converging down to a waist637 of diameter W as it propagates away from the source 630, and thendiverging thereafter. Although the beam 635 is depicted as propagatingto the substrate 660, this is not a requirement: in some examples, thesubstrate may not extend to the transverse position of the beam, or thebeam can be intercepted by a separate collector or beam dump (notshown).

The beam waist 637 is at a longitudinal coordinate Zw 639 shown measuredfrom an output port of the beam source 630. Through control of e.g.,focusing elements within the beam source 630, the working distance Zw639 can be adjusted in the longitudinal direction as indicated by arrow631. Also shown in FIG. 6 are the longitudinal coordinate Zp 649 of theprobe 645, and the longitudinal coordinate Zs 669 of the substrate 660.

In some examples, a transverse scan can be performed by moving one orboth of particle beam 635 or probe 645, as indicated by arrow 633.Current of the particle beam 635 intercepted by the probe 645 can bedirected to the ammeter 650 by wire 655 and measured, and the measuredcurrent value can be provided to the computer 610 as part of atransverse beam intercept profile. Where additional probes 645 are used,respective transverse scans and beam profiles can be obtained for eachprobe 645 or each edge of probe(s) 645. Apparatus 600 can be configuredto perform multiple scans and acquire multiple beam intercept profiles,e.g., at multiple heights of waist 637, with multiple probes 645, ormultiple configurations of beam 635, and can further evaluate the beamintercept profiles to determine one or more geometric characteristics. Asingle transverse scan can collect multiple profiles, e.g., ofrespective probe edges. A geometric characteristic can be determined byfitting the geometric characteristic to parameters derived fromtransverse beam intercept profiles.

Example Probe Height Determination

In some examples, a single nanoprobe or current collector can be used asprobe 645, and the longitudinal coordinate Zp 649 of the probe 645 canbe determined from one or more transverse scans at differentlongitudinal positions W of the beam waist 637, and the height H 647 ofthe probe 645 above the substrate 660 can be determined. Actuators 640can be driven to translate the probe 645 by the height H 647 (plus orminus an optional offset) to make contact with the substrate 660.

Example Particle Beam Tuning

In other examples, transverse scans of two probes or probe edges (or, ofone probe (edge) at two transverse positions) can be used to determinecharacteristics of the particle beam 635. These transverse scans can beat a single longitudinal position 639 of the beam waist 637. Both probes(edges) can be at a same longitudinal coordinate Zp 649, which can bethe same as the beam waist coordinate 639. The transverse scans of bothprobes (edges) can be along a common transverse axis and can beperformed together in a single scan operation. Edges of the probes canhave transverse projections which are orthogonal.

Established characteristics can include a longitudinal coordinate 639 ora diameter of a waist 637 of the particle beam 635. For example, thelongitudinal coordinate Zw 639 can be established based on twotransverse scans, above and below the waist 637, having complementaryprofiles. Midway between the two scans, the longitudinal coordinate Zw639 of the beam waist 637 can be matched to the longitudinal coordinateof the probe Zp 649. Then, with the waist 637 set to probe height(Zw=Zp), the waist diameter W can be minimized by adjusting astigmatismcontrols of the particle beam source 630. Adjusting the astigmatismcontrols can be performed by an iterative procedure and can concurrentlyreduce the beam astigmatism.

Example Apparatus Types

The apparatus 600 can be embodied and used in numerous ways. In someexamples, apparatus 600 can incorporate a scanning electron microscope(SEM), particle beam source 630 can be an SEM source, and particle beam635 can be an electron beam. In other examples, apparatus 600 can be afocused ion beam (FIB) instrument, particle beam source can be a FIBsource, and particle beam 635 can be a FIB. Probe 645 can be ananoprobe, part of a nanoprobe array, another current collector, or anedge thereof.

Example Transverse Scans

Transverse scans can be performed over a plurality of points. The pointscan be scanned successively in order of transverse position along a scanline, however this is not a requirement. In other examples, the pointscan be collected out of order, according to a predetermined pattern, orin guided iterations where one or more later scan points are selectedand measured based on measurements at one or more earlier scan points. Ascan, whether sequential or out-of-order, can be performed at a constanttransverse speed or at varying speed. In some examples, the scan speedcan be slowed down when the beam is at an edge of a probe for increaseddwell time and better signal-to-noise ratio (SNR) at the points ofinterest. The beam can be swept rapidly in between probe edges orbetween scan points.

In further examples, a transverse scan can measure one or more points todetermine a total current of the beam, and then perform guidediterations to identify specific points (e.g., 20% of total current and80% of total current) from which a measure of profile steepness can bedetermined. In varying examples, points can be measured with transversestep sizes in a range from 1 nm to 1 μm, often 10-50 nm, or about 20 nm.

Second Example Application

FIGS. 7A-7D are diagrams illustrating a second application of thedisclosed technologies. FIGS. 7A-7D illustrate transverse beam interceptprofiles 710, 720, 730, 740 obtained for respective beam characteristicswith a fixed configuration of probe edges. FIGS. 7A-7D demonstrate howtransverse beam intercept profiles 710, 720, 730, 740 can be used todistinguish among cross-sectional beam patterns 715, 725, 735, 745.Probes 701, 702 are illustrated in top view, i.e., looking along alongitudinal axis of the beam, and are oriented symmetrically at ±45°with respect to a transverse scan path 705 in the X direction. A beamscan across a probe 701, 702 can exhibit a leading edge 723 as the beambegins to be intercepted by the probe, and a trailing edge 724 as thebeam moves away from the probe. Generally, the trailing edges 724 andleading edges 723 can be symmetric for a given probe 701, 702. Keepingin mind that the beam cross-sectional dimensions can be around 1-2orders of magnitude less than the smallest transverse dimension of aprobe, the leading edge and trailing edge for a given probe can bewidely separated. Thus, to speed up a procedure, one or the other edgecan be omitted for each of the probes, that is, the transverse scan cancollect points for exactly one edge of each of the two probes 701, 702.Nevertheless, profiles across both probe edges are illustrated in FIGS.7A-7D for clarity of illustration.

In FIG. 7D, a particle beam having a tight cross-sectional pattern 745is shown. Because the illustrated beam spot is small and symmetric, thebeam current intercept profiles 741, 742 can be steep and substantiallysimilar for both probes 701, 702. However, a spreading of thecross-section in any direction can cause one or the other of theprofiles to become less steep.

In FIG. 7A, a beam with an elliptical cross-section 715 is shown, havinga major axis parallel to a length direction of probe 701. Inasmuch asthe beam cross-sectional extent parallel to the length direction ofprobe 701 has no impact on the scan profile 711 across probe 701, scanprofile 711 has steep leading and trailing edges similar to scan profile741. However, for probe 702, the top right corner of the beamcross-section (in the plane of the drawing) enters the region of probe702 at an earlier (advanced) time compared with the scenario of FIG. 7D,while the bottom left corner enters at a later (retarded) time comparedwith FIG. 7D. Accordingly, the edges of scan profile 712 are broadenedand less steep than the edges of profile 742. Thus, a beam havingastigmatism in the +45° direction can be distinguished from a tightcircular spot. Conversely, a beam having astigmatism in the −45°direction can have a broadened profile for probe 701 and a profile withsteep edges for probe 702.

Turning to FIG. 7B, another beam with elliptical cross-section 725 isshown, where the major axis of the ellipse is parallel to the transversescan direction X. In this case, profiles 721, 722 of both probes 701,702 can have broadened (less steep) edges. Thus, this beam configurationcan be distinguished from both FIGS. 7A, 7D.

FIG. 7C is similar, illustrating a beam with elliptical cross-section735, with major axis in a Y direction perpendicular to the transversescan direction X. Again, both profiles 731, 732 can be seen to havebroadened edges.

Parameters such as steepness derived from the transverse beam profiles(711 etc.) can be used to distinguish cross-sectional patterns (715etc.) of a particle beam. In examples, one or more astigmatismparameters or waist size parameters can be determined by fitting toparameters derived from the measured transverse beam intercept profiles.

Example Astigmatic Beam

FIG. 8 is a diagram depicting an example astigmatic beam 800 in anoblique view. FIG. 8 illustrates a principle of operation of someexamples of the disclosed technology.

In FIG. 8, the Z axis 805 indicates a longitudinal axis or direction ofpropagation of the beam. Three cross-sections 821-823 in transverse X-Yplanes are illustrated at respective Z coordinates, Z1-Z3. The depictedbeam 800 has a circular waist 822, with elongated ellipticalcross-sections 821, 823 above and below the waist 822.

At coordinate Z1, the elliptical cross-section 821 has a major axis atan angle of +45° to the X1 axis. At coordinate Z3, the ellipticalcross-section 823 has a major axis at an angle −45° to the X3 axis. Theaxis of elongation of an astigmatic beam can rotate 90° between abovethe waist and below the waist, and the amount of elongation (i.e., theellipse eccentricity) can be symmetric above and below the waist. Theillustrated elliptical cross-sections 821, 823 at Z1, Z3 are equidistantfrom the midplane at Z2, and are similar in size and eccentricity,differing only in orientation.

When scanned with an orthogonal probe pair, such as probes 701, 702 ofFIG. 7, the profile obtained by probe 701 at height Z1 can besubstantially similar to the profile obtained by probe 702 at height Z3,and the profile obtained by probe 702 at height Z1 can be substantiallysimilar to the profile obtained by probe 702 at height Z3. That is, atplanes symmetrically disposed above and below the waist height Z2,probes 701, 702 can have complementary beam intercept profiles. If thescanned transverse planes are not symmetric, the complementarity can belost. For example, at a Z coordinate Z4 farther below Z3 in FIG. 8, theastigmatic cross-section (not shown) can increase its eccentricity whilemaintain its major axis orientation at −45° with respect to an X axis.The profile measured by probe 701 can be broadened further, while theprofile measured by probe 702 can be narrowed further: these profilescan be distinguished from the profiles at Z3 or Z1.

In some examples, transverse scans at different Z positions relative toa waist 822 can be performed by moving the probes up or down along the Zaxis, while in other examples, the waist position can be moved byadjusting a focus control of the astigmatic beam 800 to move the waistabove and below probes 701, 702. The waist height can be unknown priorto identifying the complementary cross-sections 821, 823.

Once the complementary cross-sections 821, 823 have been identified, thewaist 822 and probes can be aligned at a common longitudinal coordinateZ. In a case with a stationary beam 800 and longitudinally translatedprobes, the probes can be set to a Z coordinate midway between Z1, Z3.In a case with variably focused beam 800 and fixed longitudinalcoordinate for the probes, a central value for a focus control can beapplied.

The central value can be between first and second value of the focuscontrol corresponding to complementary profiles 821, 823. The centralvalue can be the midpoint between the first and second values, and caninclude a correction for asymmetry in the focus control. In someexamples, the procedure can be repeated to find another set ofcomplementary profiles at Z1′, Z3′ which are closer than the originalpair Z1, Z3, i.e., |Z3′-Z1′|<|Z3-Z1|, to improve the accuracy ofdetermining or setting the waist coordinate.

Third Example Method

FIG. 9 is a flowchart 900 of a third example method according to thedisclosed technologies. In this method, transverse beam profiles can beused to tune a beam. The profiles can result from probe edgesintercepting a portion of the beam over a series of points along atransverse scan.

At process block 910, the focus of the beam can be adjusted relative toa transverse plane of the probe edges to establish the waist position atthe same longitudinal coordinate as the probe edges. At process block950, astigmatism controls of the beam can be adjusted to contract thewaist, i.e., by reducing a size or diameter of the beam waist.

Numerous variations can be used. For example, process blocks 920-934indicate an implementation of process block 910 which can be used insome examples. At process block 920, a loop can be iterated over asequence of focus settings. Block 921 indicates operations that can beperformed at each iteration of loop 920. At process block 922, atransverse beam intercept profile can be obtained on an orthogonal pairof edges (similar to profile 710). At process block 924, steepnessmeasures can be evaluated for respective probe edges traversed in theprofile.

By comparing results from different values of focus settings, a pair offocus settings having complementary profiles can be identified atprocess block 930. The complementary profiles can have steepnessmeasures for two orthogonal probe edges that are interchanged betweenthe two focus settings. From this pair of focus settings, at processblock 932 a central focus setting can be obtained, for which the beamwaist will have a same longitudinal coordinate as the probe edges. Atprocess block 934, this central focus setting can be applied, so thatthe waist position (i.e., longitudinal coordinate) can be established.

Predetermined or guided iterations can be used for loop 920, in anycombination. For example, a first set of predetermined iterations can beused to choose a first focus setting, and a second set of guidediterations can be used to locate a second focus setting having profilescomplementary to the first focus setting.

As another possible variation, process blocks 960-972 indicate animplementation of process block 950. At process block 960, a loop can beiterated over astigmatism settings. Block 961 indicates operations thatcan be performed at each astigmatism setting of loop 960. At processblock 962, a transverse beam intercept profile can be obtained on atleast one probe edge. At process block 964, a steepness measure can beevaluated for each probe edge. In some examples, guided iterations ofloop 960 can be used to home in on an astigmatism setting with minimumwaist size, and optional block 966 can be used to determine a nextastigmatism setting. In other examples, predetermined iterations can beused for loop 960 and block 966 can be omitted. In any event, once loop960 has completed, the astigmatism setting having minimum waist size canbe determined, as indicated at process block 970. By applying thisoptimal astigmatism setting at process block 972, the minimum waist sizecan be established.

In some examples, a particle beam can have two astigmatism controls, andthe method of blocks 960-972 can be applied successively, alternately,or jointly for the two astigmatism controls.

Fourth Example Method

FIG. 10 is a flowchart 1000 of a fourth example method according to thedisclosed technologies. In this method, transverse beam profiles can beused to determine geometric parameters of a particle beam. Thetransverse beam profiles can result from traversing multiple probeedges, each probe edge intercepting a portion of a particle beam over aseries of points along a transverse scan.

At process block 1010, a loop can be iterated over a sequence of currentcollector edges. The number of current collector edges can commonly betwo or four, that is, one or two edges from each of two generallyorthogonal current collectors. Two of the current collector edges canhave orthogonal transverse projections. At each iteration of the loop inblock 1010, respective transverse beam intercept profile for a presentcurrent collector edge can be obtained, i.e., a profile of particle beamcurrent intercepted by the present edge. Then, at process block 1020,the profiles from the several edges can be evaluated to determine one ormore geometric parameters of the particle beam.

Fifth Example Method

FIG. 11 is a flowchart 1100 of a fifth example method according to thedisclosed technologies. The fourth method integrates a method similar tothat of flowchart 1000 into a method for automatically tuning a particlebeam. The particle beam can be iteratively tuned as geometric parametersof the beam are determined, and corresponding control adjustments to thebeam are made. In some examples, a predetermined group of beam settingscan be evaluated together to determine a next adjustment.

At process block 1110, the locations of the current collector edges canbe determined, which can include determination of edge height,orientation, or reference position in a transverse plane, in anycombination. Process blocks 1120, 1130 can be similar to process block1010 discussed herein. At process block 1120, the particle beam istransversely scanned across the plurality of current collector edges.Concurrently, at process block 1130, transverse profiles of interceptedbeam current can be measured. Each profile can be obtained by measuringcurrent of the particle beam intercepted by a present current collectoredge at a sequence of transverse scan positions of the particle beamrelative to the present current collector edge. Alternatively, a proxyfor intercepted current can be used, as described further herein. Atprocess block 1140, the current profiles of process block 1130 can beanalyzed to determine one or more steepness measures, which areindicative of beam cross-section parameters, as described for example inthe context of FIG. 7 herein.

In some examples, the set of profiles described above for process blocks1130, 1140 can be repeated for a predetermined set of beamconfigurations. For example, with respect to a particular beamconfiguration control V, process blocks 1120, 1130, 1140 can beperformed thrice, at V={V1, V2, V3}. A control V such as a beam focuscontrol or a beam astigmatism control can be used. Other preconfiguredsets of configurations can be used, covering one, two, three, or moreconfiguration controls for the particle beam. In such examples, such aset of configurations can be regarded as an inner loop. While in such aninner loop, decision block 1150 (“Inner loop done?”) can evaluate to“no” and the method can proceed via the N branch of decision block 1150to block 1170, where a beam control adjustment is applied to reachanother predetermined configuration. To illustrate if the firstiteration of the inner loop was for a particular configuration parameterat V1, the parameter can be adjusted to V2, and then V3 at successiveiterations of process block 1170. After, the method can return toprocess block 1120 for further scanning, profile gathering, andevaluation of beam parameters.

In other examples, no inner loop is used, and each pass through processblocks 1120, 1130, 1140, leads to a new calculation of beamconfiguration parameters to obtain a “better” beam, e.g., one havinglower astigmatism or a narrower waist. In such examples, or when theabovementioned inner loop completes, the method follows the Y branchfrom decision block 1150 to decision block 1160, where a terminationcondition can be tested. An example of a termination condition can bedetermination of a second focus setting having complementary profiles toa previously selected first focus setting. Another example of atermination condition can be determination of an astigmatism settinghaving minimum beam waist size. Such determinations can be to withinpredetermined tolerances.

If the termination condition has not been met, the method can proceed toblock 1170, where a control adjustment for a new beam configuration canbe determined and applied, following which the method can revert toprocess block 1120 to reevaluate the beam cross-section parameters witha new set of beam profiles at the new beam configuration. The selectionof the new beam configuration at process block 970 can be based on asteepest descent or other optimization method. Other techniques, such assimulated annealing, can also be used.

If the termination condition has been met at block 1170, the tuningprocess (or a stage of the tuning process) can be complete, and themethod can proceed via the Y branch from block 1170 to stop block 1199.A range of termination conditions can be used, including (i) a presetnumber of passes through the blocks 1120, 1130, 1140, (ii) beam qualityparameters that meet or exceed desired beam quality parameters (e.g.,less than a threshold waist size, or less than a threshold amount ofastigmatism), or (iii) a change in beam quality parameters that is lessthan a threshold value over the last N passes through blocks 1120, 1130,1140, e.g., change in waist size less than 2% over the last four passes,or change in astigmatism less than 0.02 between last two passes. N canbe any integer greater than or equal to 2, such as 2, 3, 4, 5, or soforth. Some or all of flowchart 1100 (e.g., the loop from 1120 through1160 and 1170) can be repeated until the desired beam quality has beenachieved or some other termination condition has been met. Some or allof flowchart 1100 can be repeated for successive tuning stages, such asa first stage for establishing the waist height at a transverse plane ofthe probe edges, by adjusting a beam focus control, followed by a secondstage for establishing the waist diameter, by adjusting one or more beamastigmatism controls.

For sensitivity of the tuning procedure or ease of decouplingmeasurements or beam control adjustments, it can be desirable to use apair of transverse scan profiles across a pair of orthogonal currentcollector edges, however this is not a requirement. In other examples,other sets of transverse beam intercept profiles can be used, such as360°/N orientation steps with N probes, or two probes at anon-orthogonal angle such as 45° or 60°. In further examples, a singleprobe edge can be used, with the probe edge being rotated betweentransverse scans to emulate multiple probe edges. In additionalexamples, instead of discrete probes, a dedicated stencil can be usedhaving an array of current collector edges formed thereon at desiredangles.

Many variations are possible. In some examples, a transverse scan can beperformed with the waist of the particle beam and a current collectoredge positioned at the same longitudinal coordinate, to within atolerance. The tolerance can be in a range 0.1 mm to 1 cm, for example 1mm. Positions of the current collector edge or the waist of the particlebeam can be adjusted to match their longitudinal coordinates. Transversescans of the fourth method can be performed with uniform or varyingspeeds as described herein.

The analysis or evaluation of process block 1140 can include determiningan indicator of steepness corresponding to a portion of a particle beamintercepted by a given current collector edge as a function oftransverse coordinate. Process block 1140 can include compensating fordifferences in longitudinal position of the current collector edges.

In some examples, the fourth method can be performed with a singlecurrent collector edge, for example by changing the orientation of theedge and the scan direction between transverse scans.

Variations for Measuring Beam Profiles

In some examples, beam intercept profiles have been described in termsof a current of beam particles intercepted by a probe being measured byan ammeter. However, this is not a requirement. Alternative techniquescan be used to provide equivalent beam intercept profiles, some of whichare disclosed herein.

Complementary Measurement of Substrate Current

Current from the substrate can be measured instead of measuring probecurrent directly. The substrate current can be complementary to theprobe current, as probe current plus substrate current can equal totalparticle beam current, which can be constant. Thus, the steepness of thesubstrate current can be the same as the steepness of the probe current,and the substrate current profile can be used directly to evaluate anindicator of steepness. Alternatively, the substrate current can besubtracted from total particle beam current to infer the probe current.

Measurement of Secondary or Backscatter Particles

A particle beam impinging on a target can generate secondary orbackscatter particles. Backscatter particles can be regarded as same asthe impinging beam particles, after one or more elastic scatteringevents within the target. Secondary particles can be regarded asparticles generated within the target by an atomic or electromagneticprocess as a result of the impinging beam. The secondary particles canbe of a same type or a different type as the beam particles. Forexample, in an SEM, the beam particles and the secondary particles canboth be electrons. Alternatively, the secondary particles can be e.g.X-ray photons. In a FIB machine, the beam particles can be ions, and thesecondary particles can be electrons or photons.

Some particle beam equipment has integrated detectors for measuringsecondary or backscatter particles, often for imaging. (Such a detector,with an optional imager, 670 is shown in FIG. 6, for detecting secondaryor backscatter particles 678.) By shielding such detectors from thesubstrate, secondary or backscatter particles just from the probe can bemeasured, as the probe and particle beam are scanned transverselyrelative to one another. These measurements can be used to obtain a beamintercept profile. Alternatively, detectors can be shielded from theprobe, and complementary measurements of secondary or backscatterparticles just from the substrate can be made. These complementarysubstrate measurements can also be used to obtain a beam interceptprofile.

Direct Measurement from an Imaging Detector

In some examples, the detector intensity (e.g. current of detectedsecondary or backscatter particles) can be measured directly to obtain abeam intercept profile, as described above. In such examples, thespatial resolution of the beam intercept profile can be comparable tothe separation between neighboring points of a transverse scan.

Measurement with an Imaging Subsystem

In other examples, the detector can be coupled to an imaging subsystem,and the beam profile can be determined from pixel intensities determinedby the imaging subsystem. That is, pixel intensities of an image, e.g.one or more transverse rows of an imaging scan, can be used to obtain abeam intercept profile. A complete 2-D image is not required: pixelvalues can be determined for a single row of pixels, or a few rows, suchas 2-5 rows. Further, the beam need not be focused at the probe orsubstrate; often an unfocused or defocused beam can be used. In theseexamples, the transverse spatial resolution can be determined by theimaged pixel size. For example, with 884 pixels along a 1 μm field ofview, pixel resolution can be about 1 nm. In some examples, thisresolution can be sufficient, e.g. when the longitudinal coordinate ofthe probe is far from the beam waist. In other examples, the resolutioncan be improved (on the order of 0.1 nm or better) by reducing the fieldof view.

A Generalized Computer Environment

FIG. 12 illustrates a generalized example of a suitable computing system1200 in which described examples, techniques, and technologies can beimplemented for configuration of analytic equipment using transversebeam intercept profiles. The computing system 1200 is not intended tosuggest any limitation as to scope of use or functionality of thepresent disclosure, as the innovations can be implemented in diversegeneral-purpose or special-purpose computing systems. The computingsystem 1200 can control one or more particle beam sources, actuators,ammeters, SEM machines, FIB machines, nanoprobe test systems, otheranalytic equipment, or components thereof; or can acquire, process,output, or store measurement data.

With reference to FIG. 12, computing environment 1210 includes one ormore processing units 1222 and memory 1224. In FIG. 12, this basicconfiguration 1220 is included within a dashed line. Processing unit1222 can execute computer-executable instructions, such as for controlor data acquisition as described herein. Processing unit 1222 can be ageneral-purpose central processing unit (CPU), a processor in anapplication-specific integrated circuit (ASIC), or any other type ofprocessor. In a multi-processing system, multiple processing unitsexecute computer-executable instructions to increase processing power.Computing environment 1210 can also include a graphics processing unitor co-processing unit 1230. Tangible memory 1224 can be volatile memory(e.g., registers, cache, or RAM), non-volatile memory (e.g., ROM,EEPROM, or flash memory), or some combination thereof, accessible byprocessing units 1222, 1230. The memory 1224 stores software 1280implementing one or more innovations described herein, in the form ofcomputer-executable instructions suitable for execution by theprocessing unit(s) 1222, 1230. For example, software 1280 can includesoftware 1281 for controlling a particle beam, software 1282 forcontrolling current measurements, software 1283 for analysis, or othersoftware 1284. The inset shown for software 1280 in storage 1240 can beequally applicable to software 1280 elsewhere in FIG. 12. The memory1224 can also store control parameters, calibration data, measurementdata, or database data. The memory 1224 can also store configuration andoperational data.

A computing system 1210 can have additional features, such as one ormore of storage 1240, input devices 1250, output devices 1260, orcommunication ports 1270. An interconnection mechanism (not shown) suchas a bus, controller, or network interconnects the components of thecomputing environment 1210. Typically, operating system software (notshown) provides an operating environment for other software executing inthe computing environment 1210, and coordinates activities of thecomponents of the computing environment 1210.

The tangible storage 1240 can be removable or non-removable, andincludes magnetic disks, magnetic tapes or cassettes, CD-ROMs, DVDs, orany other medium which can be used to store information in anon-transitory way and which can be accessed within the computingenvironment 1210. The storage 1240 stores instructions of the software1280 (including instructions and/or data) implementing one or moreinnovations described herein. Storage 1240 can also store image data,measurement data, reference data, calibration data, configuration data,or other databases or data structures described herein.

The input device(s) 1250 can be a mechanical, touch-sensing, orproximity-sensing input device such as a switch, pushbutton, keyboard,mouse, pen, touchscreen, or trackball, a voice input device, a scanningdevice, or another device that provides input to the computingenvironment 1210. The output device(s) 1260 can be a display, printer,speaker, optical disk writer, digital-to-analog converter, actuator, oranother device that provides output from the computing environment 1210.Input or output can also be communicated to or from a remote device overa network connection, via communication port(s) 1270.

The communication port(s) 1270 enable communication over a communicationmedium to another computing entity. The communication medium conveysinformation such as computer-executable instructions, audio or videoinput or output, or other data in a modulated data signal. A modulateddata signal is a signal that has one or more of its characteristics setor changed in such a manner as to encode information in the signal. Byway of example, and not limitation, communication media can use anelectrical, optical, RF, acoustic, or other carrier.

A data acquisition system can be integrated into computing environment1210, either as an input device 1250 or coupled to a communication port1270, and can include analog-to-digital converters or connections to aninstrumentation bus. An instrumentation control system can be integratedinto computing environment 1210, either as an output device 1260 orcoupled to a communication port 1270, and can include digital-to-analogconverters, switches, or connections to an instrumentation bus.

In some examples, computer system 1200 can also include a computingcloud 1290 in which instructions implementing all or a portion of thedisclosed technology are executed. Any combination of memory 1224,storage 1240, and computing cloud 1290 can be used to store softwareinstructions and data of the disclosed technologies.

The present innovations can be described in the general context ofcomputer-executable instructions, such as those included in programmodules, being executed in a computing system on a target real orvirtual processor. Generally, program modules or components includeroutines, programs, libraries, objects, classes, components, datastructures, etc. that perform particular tasks or implement particulardata types. The functionality of the program modules can be combined orsplit between program modules as desired in various embodiments.Computer-executable instructions for program modules can be executedwithin a local or distributed computing system.

The terms “computing system,” “computing environment,” and “computingdevice” are used interchangeably herein. Unless the context clearlyindicates otherwise, neither term implies any limitation on a type ofcomputing system, computing environment, or computing device. Ingeneral, a computing system, computing environment, or computing devicecan be local or distributed, and can include any combination ofspecial-purpose hardware and/or general-purpose hardware and/orvirtualized hardware, together with software implementing thefunctionality described herein. Virtual processors, virtual hardware,and virtualized devices are ultimately embodied in a hardware processoror another form of physical computer hardware, and thus include bothsoftware associated with virtualization and underlying hardware.

General Considerations

As used in this application and in the claims, the singular forms “a,”“an,” and “the” include the plural forms unless the context clearlydictates otherwise. Additionally, the term “includes” means “comprises.”Further, the term “coupled” does not exclude the presence ofintermediate elements between the coupled items. Furthermore, as usedherein, the terms “or” and “and/or” mean any one item or combination ofitems in the phrase.

The systems, methods, and apparatus described herein should not beconstrued as limiting in any way. Instead, the present disclosure isdirected toward all novel and non-obvious features and aspects of thevarious disclosed embodiments, alone and in various combinations andsub-combinations with one another. The disclosed systems, methods, andapparatus are not limited to any specific aspect or feature orcombinations thereof, nor do the disclosed systems, methods, andapparatus require that any one or more specific advantages be present orproblems be solved. The technologies from any example can be combinedwith the technologies described in any one or more of the otherexamples. Any theories of operation are to facilitate explanation, butthe disclosed systems, methods, and apparatus are not limited to suchtheories of operation.

Although the operations of some of the disclosed methods are describedin a particular, sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthherein. For example, operations described sequentially may in some casesbe rearranged or performed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed systems, methods, and apparatus can be used in conjunctionwith other systems, methods, and apparatus. Additionally, thedescription sometimes uses terms like “acquire,” “actuate,” “adjust,”“analyze,” “apply,” “calculate,” “collect,” “configure,” “determine,”“dwell,” “evaluate,” “emit,” “focus,” “intercept,” “iterate,” “measure,”“move,” “obtain,” “position,” “produce,” “provide,” “scan,” “search,”“transit,” “translate,” or “tune,” to describe the disclosed methods.These terms are high-level abstractions of the actual operations thatcan be performed by or controlled by a computer system. The actualoperations that correspond to these terms will vary depending on theparticular implementation and are readily discernible by one of ordinaryskill in the art.

Theories of operation, scientific principles, or other theoreticaldescriptions presented herein in reference to the apparatus or methodsof this disclosure have been provided for the purposes of betterunderstanding, and are not intended to be limiting in scope. Theapparatus and methods in the appended claims are not limited to thoseapparatus and methods that function in the manner described by suchtheories of operation.

Any of the disclosed methods can be controlled by, or implemented as,computer-executable instructions or a computer program product stored onone or more computer-readable storage media, such as tangible,non-transitory computer-readable storage media, and executed on acomputing device (e.g., any available computing device, includingtablets, smart phones, or other mobile devices that include computinghardware). Tangible computer-readable storage media are any availabletangible media that can be accessed within a computing environment(e.g., one or more optical media discs such as DVD or CD, volatilememory components (such as DRAM or SRAM), or nonvolatile memorycomponents (such as flash memory or hard drives)). By way of example,and with reference to FIG. 12, computer-readable storage media includememory 1224, and storage 1240. The term computer-readable storage mediadoes not include signals and carrier waves. In addition, the termcomputer-readable storage media does not include communication ports(e.g., 1270).

Any of the computer-executable instructions for implementing thedisclosed techniques as well as any data created and used duringimplementation of the disclosed embodiments can be stored on one or morecomputer-readable storage media. The computer-executable instructionscan be part of, for example, a dedicated software application or asoftware application that is accessed or downloaded via a web browser orother software application (such as a remote computing application).Such software can be executed, for example, on a single local computer(e.g., any suitable commercially available computer), on an embeddedcomputer (e.g., a microprocessor, microcontroller, or specializedcomputing circuitry), or in a network environment (e.g., via theInternet, a wide-area network, a local-area network, a client-servernetwork, a cloud computing network, or other such network) using one ormore network computers.

For clarity, only certain selected aspects of the software-basedimplementations are described. Other details that are well known in theart are omitted. For example, it should be understood that the disclosedtechnology is not limited to any specific computer language or program.For instance, the disclosed technology can be implemented by softwarewritten in Adobe Flash, B#, C, C++, C#, Curl, Dart, Fortran, Java,JavaScript, Julia, Lisp, Matlab, Octave, Perl, Python, Qt, R, Ruby,Rust, SAS, SPSS, SQL, WebAssembly, any derivatives thereof, or any othersuitable programming language, or, in some examples, markup languagessuch as HTML or XML, or with any combination of suitable languages,libraries, and packages. Likewise, the disclosed technology is notlimited to any particular computer or type of hardware. Certain detailsof suitable computers and hardware are well known and need not be setforth in detail in this disclosure.

Furthermore, any of the software-based embodiments (comprising, forexample, computer-executable instructions for causing a computer toperform any of the disclosed methods) can be uploaded, downloaded,side-loaded, or remotely accessed through a suitable communicationmeans. Such suitable communication means include, for example, theInternet, the World Wide Web, an intranet, software applications, cable(including fiber optic cable), magnetic communications, electromagneticcommunications (including RF, microwave, infrared, and opticalcommunications), electronic communications, or other such communicationmeans.

The disclosed methods can also be implemented by specialized computinghardware that is configured to perform any of the disclosed methods. Forexample, the disclosed methods can be implemented by an integratedcircuit (e.g., an application specific integrated circuit (ASIC) orprogrammable logic device (PLD), such as a field programmable gate array(FPGA)). The integrated circuit or specialized computing hardware can beembedded in or directly coupled to a battery controller or anothercomputing device.

In view of the many possible embodiments to which the principles of thedisclosed subject matter may be applied, it should be recognized thatthe illustrated embodiments are only preferred examples of the disclosedsubject matter and should not be taken as limiting the scope of theclaims. Rather, the scope of the claimed subject matter is defined bythe following claims. We therefore claim all that comes within the scopeand spirit of these claims.

We claim:
 1. An apparatus comprising: a particle beam source configuredto emit a particle beam; computer-readable media storing instructions;and one or more hardware processors with memory coupled thereto, the oneor more hardware processors further coupled to the particle beam sourceand the computer-readable media; wherein the instructions, when executedby the one or more hardware processors, cause the one or more hardwareprocessors to perform operations comprising: obtaining a plurality oftransverse profiles of particle beam intensity at one or morelongitudinal positions of a waist of the particle beam; and evaluatingthe plurality of transverse profiles to establish a geometriccharacteristic.
 2. The apparatus of claim 1, wherein the obtaining agiven one of the transverse profiles comprises measuring current of theparticle beam intercepted by a current collector at a plurality ofpoints of a transverse scan of the particle beam relative to the currentcollector or of the current collector relative to the particle beam. 3.The apparatus of claim 2, wherein the current collector is a nanoprobe.4. The apparatus of claim 1, wherein the obtaining a given one of thetransverse profiles comprises measuring intensities of secondary orbackscattered particles at a plurality of points of a transverse scan ofthe particle beam relative to a probe or of the probe relative to theparticle beam.
 5. The apparatus of claim 1, wherein the obtaining agiven one of the transverse profiles comprises determining, by animaging subsystem, pixel intensities along a transverse scan of theparticle beam relative to a probe.
 6. The apparatus of claim 1, whereinthe geometric characteristic is a longitudinal coordinate of a probe. 7.The apparatus of claim 6, wherein the probe is a nanoprobe, and furthercomprising: an actuator coupled to the nanoprobe; wherein the operationsfurther comprise: determining a longitudinal translation of thenanoprobe based on a difference between the longitudinal coordinate ofthe nanoprobe and a longitudinal coordinate of a substrate surface; andcontrolling the actuator to place the nanoprobe in contact with thesubstrate surface based on the determined longitudinal translation. 8.The apparatus of claim 1, wherein the geometric characteristic is alongitudinal coordinate of the waist of the particle beam.
 9. Theapparatus of claim 8, wherein first and second profiles of the pluralityof transverse profiles respectively comprise transverse scan points ofthe particle beam relative to first and second probe edges or of thefirst and second probe edges relative to the particle beam, wherein thefirst and second probe edges have orthogonal transverse projections. 10.The apparatus of claim 9, wherein the first and second profiles areobtained in a single transverse scan, and a scan speed of the singletransverse scan is faster when the particle beam is at one of the twoprobe edges than when the particle beam is between the two probe edges.11. The apparatus of claim 9, wherein the operations further comprise:executing a control adjustment on the particle beam to reduce anastigmatism or a waist size of the particle beam.
 12. The apparatus ofclaim 1, wherein the apparatus is a scanning electron microscope. 13.The apparatus of claim 1, wherein the particle beam is a focused ionbeam.
 14. A method comprising: obtaining a plurality of transverse beamintercept profiles for respective longitudinal positions of a waist of aparticle beam, each of the transverse beam intercept profiles obtainedwith a probe at least partly intercepting the particle beam; andevaluating the transverse beam intercept profiles to determine alongitudinal coordinate of the probe.
 15. The method of claim 14,wherein the obtaining comprises measuring current of the particle beamintercepted by the probe at a plurality of points of a transverse scanof the particle beam relative to the probe.
 16. The method of claim 14,wherein the evaluating further comprises: determining an indicator ofsteepness, for each of the transverse beam intercept profiles;determining a first longitudinal coordinate of the waist of the particlebeam, at which the steepness is a maximum, by fitting a measure of thesteepness as a function of the respective longitudinal positions of thewaist of the particle beam; and determining the longitudinal coordinateof the probe based on the first longitudinal coordinate.
 17. The methodof claim 14, wherein the evaluating further comprises: determining anindicator of steepness, for each of the transverse beam interceptprofiles; determining a first longitudinal coordinate of the waist ofthe particle beam, at which the steepness is a maximum, by iterating thelongitudinal positions of the waist of the particle beam until aconvergence criterion is met; and determining the longitudinalcoordinate of the probe based on the first longitudinal coordinate ofthe waist of the particle beam.
 18. The method of claim 14, wherein thetransverse beam intercept profiles are first transverse beam interceptprofiles, and further comprising: tuning a cross-sectional pattern ofthe particle beam prior to the obtaining, based on a plurality of secondtransverse beam intercept profiles.
 19. The method of claim 14, furthercomprising: determining an amount of longitudinal translation for theprobe from a difference between the longitudinal coordinate of the probeand a longitudinal coordinate of a substrate surface; and causing theprobe to be longitudinally translated by the determined amount.
 20. Themethod of claim 19, wherein: the obtaining comprises measuring currentof the particle beam intercepted by the probe at a plurality of pointsof a transverse scan of the particle beam relative to the probe; theevaluating comprises: determining an indicator of steepness, for each ofthe transverse beam intercept profiles, corresponding to a portion ofthe particle beam intercepted by the probe as a function of a transversecoordinate; determining a first longitudinal coordinate of the waist ofthe particle beam at which the steepness is a maximum; and determiningthe longitudinal coordinate of the probe based on the first longitudinalcoordinate; the particle beam is an electron beam of a scanning electronmicroscope; and the probe is a nanoprobe.
 21. One or morecomputer-readable storage media storing instructions which, whenexecuted by one or more hardware processors, cause the one or morehardware processors to perform the method of claim
 14. 22. A methodcomprising: obtaining a plurality of transverse beam intercept profilesfor respective probe edges having distinct orientations, each of theprofiles with the respective probe edge at least partly intercepting aparticle beam; and evaluating the transverse beam intercept profiles toestablish one or more geometric parameters of the particle beam.
 23. Themethod of claim 22, wherein the obtaining comprises measuring current ofthe particle beam intercepted by a given one of the probe edges at aplurality of positions of a transverse scan of the particle beamrelative to the given probe edge.
 24. The method of claim 22, whereinthe one or more geometric parameters comprise a longitudinal coordinateof a waist of the particle beam, wherein the establishing thelongitudinal coordinate comprises setting the longitudinal coordinate ata transverse plane of the probe edges and wherein the method furthercomprises: adjusting one or more astigmatism controls to contract thewaist of the particle beam.
 25. The method of claim 22, wherein two ofthe probe edges have orthogonal transverse projections, and theevaluating comprises: identifying first and second values of a focuscontrol of the particle beam at which the transverse beam interceptprofiles of the two probe edges are complementary.
 26. The method ofclaim 25, wherein: the obtaining comprises measuring current of theparticle beam intercepted by a given one of the two probe edges at aplurality of positions of a transverse scan of the particle beamrelative to the given probe edge; the particle beam is an electron beamof a scanning electron microscope and has a waist; the two probe edgesare edges of one or more nanoprobes; the plurality of positions aredisposed in a straight line; the one or more geometric parametersinclude a longitudinal coordinate of the waist and a diameter of thewaist; and the method further comprises: determining a central valuebetween the first and second values; establishing the longitudinalcoordinate of the waist at a transverse plane of the two probe edges bysetting the focus control to the central value; and iterating oversettings of one or more astigmatism controls of the particle beam tominimize the diameter of the waist.
 27. One or more computer-readablestorage media storing instructions which, when executed by one or morehardware processors, cause the one or more hardware processors toperform the method of claim 22.